Insulator supporting pin



F. P. SEXTON INSULATOR SUPPORTING FIN June 1, 1937.

Filed Oct. 1, 1934 INVENTOR EP-SEXTON gQfZ ATTORNEY Patented June 1,1937 UNITED. STATES PATENT OFFICE Application October 1,

3 Claims.

In order to realize the full mechanical strength of a porcelaininsulator and to prevent diificulties due to radio interference, it isnecessary to screw the insulator home until the top of the pin hole isbrought in contact with the upper end of the lead head or mantle of thesupporting pin. With the pins now in use this is often impossible owingto irregularities in the pin hole due to shrinkage and distortion of theporcelain during the firing process. In such instances the gap leftbetween the pin and the top of the pin hole not only results in loss ofmechanical strength but also gives rise to radio interference. It alsofrequently happens that the top groove of the insulator is not properlylined up when the insulator is screwed home. To correct this conditionthe insulator must be backed off or else the pin must be moved in thecross arm to which it is attached. Owing to the taper of the pin holeand the engaging threaded portion of the pin it is not desirable to backoff the insulator after it is once screwed home, since this loosens theinsulator and also leaves an undesirable gap between the top of the pinhole and the top of the pin. The movement of the pin in the cross arm toline up the insulator groove is also objectionable on account of thetrouble involved.

The present invention provides a pin designed to overcome the abovementioned difficulties and to ensure perfect seating of the insulatorthereon regardless of whether the pin hole in the insulator is true orhas been distorted by shrinkage during the firing process. An importantfeature of the invention consists in the provision of soft metalprojections at the upper end of the pin adapted to be engaged by the topof the pin hole when the insulator is screwed home. These projectionsensure a proper ground connection between the pin and the top of theinsulator while providing sufficient clearance for expansion purposes.Being made of soft metal capable of flowing under pressure they alsoenable the top groove of the insulator to be properly lined up withoutbacking off the insulator or resorting to the troublesome practice ofmoving the pin in the cross arm. In this connection it may be explainedthat, while the insulator may be considered to be screwed home as soonas the top wall of the pin hole contacts the tips of the projections,the latter will flow, under pressure, to permit such slight furtherscrewing on of the insulator as may be necessary to line up theinsulator groove. Another feature consists in providing the pin with astarting thread located below 1934, Serial No. 746,315

said projections immediately in advance of a non-threaded soft metalportion in which the insulator cuts its own thread as it is screwedhome. This ensures perfect seating of the insulator regardless ofwhether the pin hole is true or distorted. A still further feature,which is optional, consists in providing the pin with a further threadedportion adapted to be engaged by the internal thread of the insulatorafter the latter has cut its way through the soft metal portionadjoining the starting thread.

The foregoing and other features and advantages of the invention will bemore readily understood from the following detailed description taken inconnection with the accompanying drawing, in which Fig. 1 is a verticalsectional view through an insulator mounted on a pin constructed inaccordance with a preferred embodiment of the present invention.

Fig. 2 is a top plan View of the insulator supporting pin.

Fig. 3 is a view, in side elevation, of the insulator supporting pin.

Fig. 4 is a view similar to Fig. 3 but showing a slight modification.

In the construction shown in Figs. 1 to 3 inclusive, 5 designates aconventional insulator pin having a lead mantle 6 cast on or otherwisesecured to its upper end. The mantle has a slight inward taper towardsits upper end on which are formed four vertical projections 5a which, inthe form shown, taper to a point at their upper ends. The mantle is alsocast or otherwise provided with upper and lower threaded portions 1 and8 separated by a non-threaded intermediate portion shaped to present aseries of laterally spaced lengthwise extending ribs 9. These ribs arearranged so that the insulator in cuts its own thread therein as it isscrewed home against the projections 5a following initial engagement ofthe insulator thread II with the starting thread I. In the case: ofrelatively long insulators, such as that shown in Fig. 1, the insulatorthread I I is preferably engaged with the bottom thread 8 of the mantleafter cutting its way through the ribs 9. However, the threaded portion8 at the lower end of the mantle is not absolutely essential and may bedispensed with as shown in Fig. 4, in which the ribs 9 extend from thestarting thread I to the lower end of the mantle. When relatively shortinsulators are used with a pin of the type shown in Fig. 4, the ribs 9may be made shorter so that their lower ends terminate any desireddistance above the lower end of the mantle. As soon as the insulator isscrewed home to the point where the top of the pin hole bears againstthe tips of the projections 5a, a satisfactory ground connection isestablished between the pin and the top of the insulator. At the sametime, a perfect seating of the insulator on the pin is obtained due tothe fact that the threads cut in the ribs 9 conform exactly to theinsulator thread. In order to properly line up the insulator groove aslight further screwing on of the insulator may be necessary after thetop Wall of the pin hole is engaged with the tips of the projections 5a.This, however, is easily accomplished owing to the fact that the saidprojections are made of soft metal capable of flowing under pressureand, hence, may be compressed between the top portions of the mantle andthe pin. hole, as shown in Fig. 1. In some insulators the top portion ofthe pin hole is made dome-shaped and, with this in view, the outer sidesof the projections 5a are curved longitudinally so that they will becrowded inwardly as they are compressed between the insulator and thedome-shaped upper portion of the pin hole. The spacing of theprojections 5a is important in that, even when the projections arecompressed as shown in Fig. 1, sufficient space is left therebetween forexpansion purposes.

Having thus described what I now conceive to be the preferredembodiments of my invention, it will be understood that variousmodifications may be resorted to within the scope and spirit of theappended claims and that the various features of improvement may be usedsingly as well as in combination. For example, the addition of the softmetal top projections 5a to the externally threaded lead head of anotherwise conventional supporting pin would ensure a proper groundconnection between the pin and the top of the insulator in addition toits advantages with respect to lining up the insulator groove. Likewise,the shaping of the lead head or mantle of an insulator supporting pin toprovide a starting groove in advance of a nonthreaded soft metal portionin which the insulator cuts its own thread would be an improvement evenin the absence of the projections 5a.

Having thus described my invention, what I claim is:

1. An insulator supporting pin provided with a mantle of soft metalshaped to present a starting thread above one or more non-threadedaxially extending ribs of soft metal in which a continuation of thelower end of the starting thread is cut by the insulator thread as theinsulator is screwed home after being initially engaged with thestarting thread.

2. An insulator supporting pin provided with a mantle of soft metalshaped to present upper and lower threaded portions including a seriesof laterally spaced axially extending ribs in which the insulator cutsits own thread as it is screwed home after being initially engaged withsaid upper threaded portion.

3. An insulator supporting pin provided with a mantle of soft metalcovering the top and upper side surfaces of the pin, said mantle havinga starting thread formed therein in advance of a non-threaded soft metalportion in which a continuation of the starting thread is cut by theinsulator as it is screwed home, and a plurality of projections formedintegral with the top portion of said mantle and projecting upwardlytherefrom, each of said projections tapering to a point and being spaceda substantial distance from each of the remaining projections.

FREDERICK P. SEXTON.

